Fluoropolymers, i.e. polymers having a fluorinated backbone, have been long known and have been used in a variety of applications because of several desirable properties such as heat resistance, chemical resistance, weatherability, UV-stability etc.
A frequently used method for producing fluoropolymers involves aqueous emulsion polymerization of one or more fluorinated monomers generally involving the use of fluorinated surfactants. Frequently used fluorinated surfactants include perfluorooctanoic acids and salts thereof, in particular ammonium perfluorooctanoic acid.
Recently, perfluoroalkanoic acids having 8 or more carbon atoms have raised environmental concerns. For instance, perfluoroalkanoic acids have been found to show bioaccumulation. Accordingly, efforts are now devoted to phasing out from such compounds and methods have been developed to manufacture fluoropolymer products using alternative surfactants having a more favourable toxicological profile.
Several approaches have been recently pursued to this aim, typically involving fluorosurfactants comprising a perfluoroalkyl chain interrupted by one or more catenary oxygen atoms, said chain having an ionic carboxylate group at one of its ends.
Examples of these compounds which are endowed with improved bioaccumulation profile over perfluoro alkanoic acids having 8 or more carbon atoms can be found notably in US 2007276103 (3M INNOVATIVE PROPERTIES CO) 29, Nov. 2007, US 2007015864 (3M INNOVATIVE PROPERTIES CO) 18, Jan. 2007, US 2007015865 (3M INNOVATIVE PROPERTIES CO) 18, Jan. 2007, US 2007015866 (3M INNOVATIVE PROPERTIES CO) 18, Jan. 2007.
It would thus be desirable to find alternative fluorinated surfactants that can be used in the emulsion polymerization of fluorinated monomers which desirably show lower bioaccumulation/biopersistence than perfluoro alkanoic acids having 8 or more carbon atoms.
It would further be desirable that the surfactant properties of said alternative fluorinated surfactants be such that polymerization can be carried out in a convenient and cost effective way, using equipment commonly used in the aqueous emulsion polymerization of fluorinated monomers with traditional surfactants.